The present invention relates to a solid state imaging device, a method for driving the same, and a camera, and more particularly, it relates to a solid state imaging device for use in a high-definition camera or the like, a method for driving the same, and a camera using the same.
FIG. 7 shows an exemplified conventional solid state imaging device including MOS transistors. As shown in FIG. 7, the solid state imaging device has an imaging area 120 where a plurality of amplifying unit pixels are two-dimensionally arranged. Each amplifying unit pixel includes a photodiode (PD) portion 111; a floating diffusion portion (FD) 117 connected to the PD portion 111 through a read transistor 112 for storing charge read from the PD portion 111; a reset transistor 113 for initializing the state of the FD portion 117; and a detection transistor 114 connected to the FD portion 117 for controlling the signal output of the pixel.
Each row of the amplifying unit pixels is selected by a vertical shift register 141 operated in accordance with a drive timing pulse sent from a timing generator circuit 140. Signals of the amplifying unit pixels of the selected row are stored in row memories 123. Thereafter, a horizontal shift register 142 is driven by a drive timing pulse sent from the timing generator circuit 140, so that the pixel signals stored in the row memories 123 can be successively output as device signals from an output amplifier 127 through a horizontal signal line 126.
FIG. 8 is a timing chart in a horizontal drive period besides a vertical blanking period of the conventional solid state imaging device. A horizontal drive period is composed of a horizontal blanking period and a horizontal active period. The horizontal blanking period starts at timing T1, a reset pulse is applied, at timing T2, to a reset pulse line 132 on an nth row (wherein n is a positive integer) with a voltage of a VDD power supply 116 set to a high (H) level, so as to simultaneously reset the FD portion 117 and select the detection transistor 114 on the nth row. Thereafter, a read pulse is applied to a read pulse line 131 at timing T3, so as to read the charge of the PD portion 111 to the FD portion 117. A signal corresponding to the read charge is stored in the row memory 123 through the detection transistor 114. Then, a reset pulse is applied, at timing T5, to the reset pulse line 132 on the nth row with the voltage of the VDD power supply 116 set to a low (L) level, so as to set the potential of the FD portion 117 to a low level and place the detection transistor 114 on the nth row in an unselected state. The signals stored in the row memories 123 are successively output from the solid state imaging device by operating the horizontal shift register 142 during the horizontal active period.
In this manner, in the solid state imaging device having one row memory for one row of pixels correspondingly to each horizontal signal line 126, images are generally drawn by reading signals from pixels and storing them in memories in a horizontal blanking period included in a horizontal drive period besides a vertical blanking period and outputting the signals from the row memories in a horizontal active period included in the horizontal drive period besides the vertical blanking period (see, for example, Japanese Laid-Open Patent Publication Nos. 9-163234 and 4-877).
In the conventional solid state imaging device, if signals are read from pixels and the read signals are stored in row memories in the horizontal active period included in the horizontal drive period besides the vertical blanking period, signals of pixels on an (n+1)th row are overwritten on signals of pixels on the nth row remaining in the row memories 123, and therefore, an accurate image cannot be obtained and the image is disadvantageously degraded.
Although the horizontal drive period besides the vertical blanking period is described above, since an image is basically not drawn in the vertical blanking period, pixel signals may be read and the read signals may be stored in row memories in the horizontal active period included in the horizontal drive period as an exception.
In driving a solid state imaging device for a high quality high-definition image, however, all of the horizontal blanking period, the horizontal active period and the horizontal drive period as a sum of the horizontal blanking period and the horizontal active period are much shorter than in conventional technique. Therefore, it is necessary to rapidly perform an operation for reading signals from pixels and storing the read signals in row memories and an operation for outputting the signals from the row memories in a solid state imaging device for a high-definition image. Accordingly, signals stored in row memories exhibit unstable values, and hence, there arises a problem that the quality of an image created in accordance with the signals read from the row memories is largely degraded.